Discrepancies Between Mechanical and Sonic Shear Methods in Evaluating Shear Stability of Hydraulic Fluids.

摘要

Method and equipment effects on shear stability measurements employing sonic and mechanical methods were determined using commercial hydraulic oils conforming to Military Specifications MIL-H-13866A, MIL-H-13919A, and MIL-H-5606. An interlaboratory, cooperative test program included the sonic shear stability method and two mechanical shear stability methods. In addition, experimental variations in the sonic shear test procedure were made to explain the discrepancies between sonic and mechanical test results. Interlaboratory test work indicated the sonic shear method showed good reproducibility, while rating five of six test fluids less shear stable than a shear reference fluid. The two mechanical shear methods did not show good reproducibility, but agreed in rating four of five test fluids more shear stable than the reference fluid. The mechanical methods were generally more effective in shearing this reference fluid than the test fluids, while the reverse was true for the sonic tests. Experimental variations of some of the sonic shear test parameters affected shear test results; however, these effects did not explain differences between sonic and mechanical test results. These discrepancies could only be attributed to differences in both chemical type and molecular weight of the polymer thickeners used in the various fluids.